State media says regime army enters town of Manbij in northern Syria

The Syrian regime army entered the town of Manbij in northern Syria on Monday, Syrian state-run TV and news agency said.

On Monday, Russian-backed Syrian government forces wasted no time in taking advantage of an abrupt U.S. retreat from Syria after the Turkish incursion, deploying deep inside Kurdish-held territory south of the Turkish frontier.

In its turn, the United States said Monday it was appalled and seeking more information after accounts that pro-Turkish fighters in Syria have summarily executed civilians including a female Kurdish politician.

The Kurdish-dominated Syrian Democratic Forces said that at least nine civilians were "executed" as part of Turkey's invasion that it launched Wednesday against the former US allies.

Among them was 35-year-old Hevrin Khalaf, the secretary-general of the Future Syria Party, who according to the forces was taken out of her car and killed by Turkish-allied Syrian forces.

"We find these reports to be extremely troubling, reflecting the overall destabilization of northeast Syria since the commencement of hostilities," a US State Department official said.

"We condemn in the strongest of terms any mistreatment and extrajudicial execution of civilians or prisoners, and are looking further into these circumstances," the official said on condition of anonymity.

Defense Secretary Mark Esper, in an interview Sunday on CBS, said that a grisly video purportedly of Khalaf's killing could not be confirmed but, if true, the killings of civilians "would be war crimes."

The Syrian Democratic Forces spearheaded the fight against the Islamic State group in alliance with the United States.

But Turkey links them to Kurdish separatists at home and President Recep Tayyip Erdogan ordered the operation after speaking to President Donald Trump, who pulled out US troops who served as a buffer.

The State Department official said that the United States on Sunday also pulled out of Syria civilian officers who were working on stabilization.

Trump says that the United States no longer has a need a presence in Syria after fighting the Islamic State group and should instead focus at home.

Representative Veronica Escobar, a Democrat, pointed to Khalaf's killing as she denounced Trump as a "dangerous man" and, echoing retired US general John Allen, said he had "blood on his hands."